Sounds like your access authority has been corrupted - you have two alternatives - the first is go on a witch hunt and find out what is wrong or you can simply delete the user profile and start again.
Having got in a lot of trouble once before trying to correct user privileges that had been corrupted I definitely recommend the later.
Backup all your user data in this account and then delete the account - and then start again by creating a new account.
The only thing (if I was you) is to change the account to limited (settings\user accounts) and then reboot - and then change the account back to administrative privilege to see if you can reset the settings.
I have 3 hard drives hooked up to windows xp2 prof.
The 2 HD's are normal inside the case. The 3rd is an external 120 WD (all are WD drives). he 3rd is partitioned into 2 logical drives q/s. I have 2 users plus the admin desktop. My main user will not allow me to work with the 3rd drive. I get a message that "This operation has been cancelled due to restrictions in effect on this computer. Please contact your administrator."
This is a single computer with all users having administrator privileges. By going to one of the other users I'm able to work with the 3rd drive.
It's driving me to distraction. Can anyone help me solve this problem.